The invention relates to a ball joint for a rod, especially a telescopic rod for an external fixator, especially for use with an external ring fixator. It is further related to a strut comprising a rod and two ball or universal joints at the free ends of the rod.
A plurality of compression-distraction apparatus have been designed and improved by Ilizarov and his group using two external rings to be placed around the limb to be fixed. There are usually at least two such rings, one proximal and one distal ring, which are connected with a plurality of struts or rods. Preferably, these struts are linked to the rings in a way that the attachment points can be pivoted and the length of the strut can be varied to enable adjustment of the external fixation rings.
Ilizarov has also provided some improvements for said systems. EP 0 377 744 shows a telescopic rod for such an external fixator. U.S. Pat. No. 4,615,338 shows a further device to control the length of such telescopic rods. The rods are extending through the rings and are attached to said rings via nuts. The use of said devices is inconvenient since the two rings, between which the struts are to be arranged, need to be in nearly perfect orientation to fit the straight rods through the ring holes of said rings.
A different external ring fixator having telescopic rods is shown in U.S. Pat. No. 5,702,389. There the connection between the rods and the two related rings use a different structure. That patent discloses spheres incorporated into the ring system, being half-spheres attaching two rods to such a hole. Further, in order to achieve adjustability, one part of the connector is introduced into a hole of the fixator ring and consists of a flexible material which then attaches to the rod part of the strut. This allows for pivotal connection of said rod/strut to one hole of the ring of the fixator.